1. Field of the Invention
The invention relates to an apparatus and method used in chemical vapor deposition (CVD) of films using a gas or plasma, and more particularly, to a dual plenum “showerhead” apparatus and method of depositing a gas mixture using chemical vapor deposition.
2. Description of Related Art
Typically, the chemical vapor deposition (CVD) occurs in a reaction process chamber or reactor chamber that provides a low-conductance, contaminant-free environment for flowing gases or plasma over the substrate in a uniform manner. Alternatively, CVD may be performed in a high-conductance reaction process chamber that provides a relatively large flow of process gas to achieve a uniform film deposition.
Generally, in CVD processes, gaseous reactants are introduced into the reaction process chamber whereby they decompose and react at a heated surface of a substrate to form a desired film thereon. The CVD films are deposited on wafers in a controlled environment in the reaction chamber to provide controlled thin-film depositions, as well as thin film etching and surface treatments, such as, cleaning. In so doing both the CVD plasma deposition and plasma etch processes occur within the reaction chamber to either deposit a film onto surfaces of a wafer or remove a film on a wafer contacting the plasma by etching. In the fabrication of microelectronic devices, CVD is often the preferred process for depositing thin films on substrates due to its ability to provide highly conformal layers even in deep contacts and other openings. For example, CVD processes are used for depositing materials on substrates to fabricate semiconductor IC chips.
Known processes of plasma CVD and plasma etch occurring within a reactor chamber may include a pair of electrodes and a radiofrequency source which, in combination, generates a discharge between the electrodes to ionize reactive gases therein. These ionized gases form a plasma which deposits the non-volatile solid film onto the substrate by the reaction of vapor phase reactants, or etches the film off of, surfaces in contact with the plasma. For example, in plasma CVD, a semiconductor wafer is clamped to one of the electrodes so that selected films can be deposited onto a workpiece surface exposed to the plasma between the electrodes. Successive exposures to differing plasmas can create desirable semiconductor films on the surface. Similarly, in plasma etch, coatings or films can be removed selectively when exposed to plasmas formed by appropriate etch gases, e.g., carbon tetrafluoride.
Additionally, high voltage electrodes, arranged with a plurality of gas outlets, may extend there-through the reaction chamber so that reactive gases may be injected through the outlets and between the electrodes to uniformly distribute gases over the surface of a workpiece. The outlets are generally a series of holes extending through the electrode and connected to the appropriate gas source. Typically, high voltage electrodes in this type of configuration are referred to as a “showerhead” electrode because of its appearance and similarity to a common bathroom showerhead.
Conventional CVD systems use a showerhead arrangement to alleviate the deposition of a bell-shaped film thickness. Typically, such bell-shaped film thickness is formed as a result of single wafer CVD systems feeding gases above and perpendicular to a substrate wafer whereby the center of the substrate tends to receive a higher concentration of process chemicals, resulting in faster thin-film material growth at the center of the substrate than at the edges. The showerhead arrangements alleviate this difficulty by flowing the precursor gas from above the showerhead into a centrally-located inlet of the showerhead housing. In so doing the showerhead typically has a showerhead gas dispersion plate including several hundred small openings to allow a low-conductance flow of the gases to the CVD reaction chamber for more uniform distribution across the substrate.
However, such conventional showerhead arrangements disadvantageously emit high concentrations of one gas from a nozzle or post of the CVD system within specific areas in the reaction chamber. Such high concentrations of one gas is undesirable within the reactor since thorough mixing of multiple gases in the CVD reactor facilitates and improves the deposition of the gases or plasma to form a film on the wafer surface. Another disadvantage may occur when there is insufficient gas mixing in front of the orifices emitting the gases into the reactor. In such situations, a build-up of unwanted deposits may occur on the showerhead including, for example, a high carbon film. Such unwanted deposits on the showerhead are undesirable as they are difficult to remove and they etch very slowly. Furthermore, these unwanted deposits may interfere with the desirable intermixing of the desired emitted gases such as, for example, the intermixing of NH3 and TDEAT, to lessen the deposition rate of such mixed gases on the wafer, thereby negatively affecting the efficiency and reliability of the CVD film process.
Accordingly, a need continues to exist in the art for improved CVD systems and processes which decrease the build-up of unwanted deposits on a showerhead and which effectively and efficiently mix desired gases in front of the orifices emitting such gases into the reaction chamber to improve the deposition thereof and thereby form conformal films on a wafer surface.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved showerhead apparatus and method which more effectively and efficiently mix gases in a CVD reactor chamber.
It is another object of the present invention to provide a showerhead apparatus and method which encourage mixing of desired gases in front of the orifices emitting such gases into the CVD reactor chamber.
Another object of the present invention is to provide a showerhead apparatus and method which minimize unwanted particle levels on a face area of the showerhead and on the tip of a gas outlet.
It is a further object of the present invention to provide a showerhead apparatus and method which form a conformal film on a wafer surface in a CVD process.
Still another object of the present invention is to provide a showerhead apparatus and method which improve the efficiency and reliability of a CVD film process.
Yet another object of the present invention is to provide a showerhead apparatus and method which improves the utilization of the deposition materials.
Another object of the present invention is to provide a showerhead apparatus and method which allow for easier and faster cleaning of the showerhead faceplate and the tip of the gas outlet after the deposition process.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.